Oxytocin response to insulin-induced hypoglycemia in obese subjects before and after weight loss

Abstract

The response of plasma oxytocin to an iv bolus injection of crystalline insulin (0.15 U/kg) was evaluated in 14 normal weight [mean body mass index (BMI) = 23] and in 9 obese (mean BMI = 42) men. Similar blood glucose decrements after insulin injection were observed in the two groups. Obese and normal weight subjects presented similar basal oxytocin levels. In both groups, oxytocin rose significantly during the insulin tolerance test (ITT); however, the peak oxytocin response in the obese men was significantly lower than in the normal weight subjects. Obese men were restudied after substantial weight loss. Basal oxytocin levels and glucose response to insulin did not change after weight reduction. The oxytocin response to the ITT was significantly higher than before slimming and did not differ from that observed in the normal weight subjects. A significant negative correlation between BMI values and oxytocin peak levels during ITT was observed in the lean controls and obese subjects (r = 0.516, p less than 0.02). These results demonstrate that in obese subjects the oxytocin secretory response during an insulin tolerance test is reduced, suggesting the existence of a hypothalamic-pituitary disorder in obesity.

Plasma Oxytocin Concentration in Pre- and Postmenopausal Women: Its Relationship with Obesity, Body Composition and Metabolic Variables

“…In this regard, we hypothesize that the high BMI values of our obese patients could have yielded a broad bulky effect on oxytocin secretion. To date, oxytocin levels in obesity have been found decreased [18], unchanged [41], or even increased [24] as compared to controls. Several reasons could contribute to explain these discrepancies, such as differences in study cohorts, gender prevalence, degree of obesity, sampling procedures, and analytical methodologies [21,28].…”

Relationship between Plasma Profiles of Oxytocin and Adrenocorticotropic Hormone during Suckling or Breast Stimulation in Women

“…The tubes were placed in an ice bath and centrifuged in the cold; the plasma was separated and stored at -2 0 °C until assayed. Plasma OT [15,16], ACTH [17] and cortisol [18] concentrations were measured with specific ra dioimmunoassay (R1A) methods. All samples from the same sub jects were measured in duplicate in the same assay.…”

Hypoglycemia-Induced Arginine Vasopressin and Oxytocin Release Is Mediated by Glucoreceptors Located Inside the Blood-Brain Barrier

“…Plasma AVP [15] and OT [3,15] were measured by specific R1A methods, as previously described. The limits of detection of the AVP and OT assays were 1.2 and 2.0 pg/ml, respectively.…”

“…These data exclude a di rect role of hyperinsulinemia in the mechanism underlying the AVP and OT responses during ITT. Furthermore, since glucose, but not fructose, crosses the blood-brain barrier (BBB), the posterior pituitary hormone responses to hypoglycemia appear to be generated by stimulations of glucosensitive areas located inside the BBB.Insulin-induced hypoglycemia is a primary stimulus for the secretion of both posterior pituitary hormones ar ginine vasopressin (AVP) and oxytocin (OT) [1][2][3]. Even though a direct action of insulin at the hypothalamic level has been reported [4][5][6][7], normoglycemic hyperinsuliné mie clamp studies have demonstrated that hyperinsuline mia does not promote vasopressin secretion [8], There fore, the AVP and OT responses during an insulin toler ance test (ITT) are supposed to follow direct stimulation of hypothalamic glucoreceptors [4][5][6][7] elicited by the neuropenic symptomatic stimulus [9][10][11][12].…”